1. Field of the Invention
The present invention relates to adhesives, and more particularly, to adhesives for connecting semiconductor chips to a substrate.
2. Description of the Prior Art
Adhesives including a thermosetting resin, such as an epoxy resin, has traditionally been used for attaching semiconductor chips to a substrate.
In an electric device, generally denoted by reference numeral 101 in FIG. 7, a semiconductor chip 111 is adhered to a substrate 113 by an adhesive 112. A bump-like terminal 121, which is arranged on the semiconductor chip 111, is in contact with a terminal 122, which is a part of a wiring pattern on the substrate 113. In the state shown, an internal circuit within the semiconductor chip 111 is electrically connected to the wiring pattern on the substrate 113 via the terminals 121 and 122. A thermosetting resin in the adhesive 112 is cured to mechanically connect the semiconductor 111 to the substrate 113.
The adhesive 112 typically includes a curing agent such as a microcapsulated imidazole for curing the epoxy resin.
The adhesive using such a curing agent must be heated to a temperature of 180° C. or above to be cured. Such a high temperature condition may damage the wiring pattern on the substrate 113 when the wiring pattern is finely formed. A low heating temperature requires a prolonged heat treatment though the damage caused by heat may be reduced.
In recent years, adhesives including a radical polymerizable resin, such as an acrylate, and a radical polymerization initiator have been developed. While these adhesives are readily curable at a relatively low temperature, the electrical characteristics and heat-resistance they exhibit when cured are not as good as adhesives using thermosetting resins. For this reason, the electrical device 101 constructed using such adhesives tends to be less reliable.